A personal connection to a Mueller witness is unlikely to sway Whitaker or the White House when it comes to recusal, as Deputy Attorney General Rod Rosenstein supervised the probe despite being a witness himself. The agency did not announce a departure for Rosenstein, who appointed Mueller and has closely overseen his work.
Whitaker, a former USA attorney for the Southern District of Iowa, had served as Sessions's chief of staff since September 2017. Whitaker did, however, believe that Sessions had no choice but to recuse himself from the matter, the person said.
What does this mean for the Mueller probe?They include his former National Security Adviser, Michael Flynn, and his former lawyer, Michael Cohen. It culminated in the White House later banning a CNN reporter who questioned the President aggressively on why he insisted on calling a migrant caravan that is hundreds of miles from the United States border an 'invasion'.
In a resignation letter, Mr Sessions - a former Alabama senator who was an early supporter of Mr Trump - made clear the decision to go was not his own.
Democrats also raised concerns about the appointment of Whitaker, 49, who will now oversee Mueller's probe.
"I could fire everybody right now, but I don't want to stop it because politically I don't like stopping it", Mr Trump told a White House news conference. He looked close to tears as he was applauded by the staff on his way out of the justice department building on Wednesday night.
During a brief stint past year as a conservative legal commentator on CNN, Whitaker often appeared as a Trump defender, saying he saw no evidence the president colluded with Russians during the 2016 campaign or obstructed justice. Schumer and Democrat Nancy Pelosi, who is likely to become House speaker next year, called on Whitaker to recuse himself, with Schumer citing "his previous comments advocating defunding and imposing limitations on the Mueller investigation".
Under the special counsel regulations, the attorney general must notify the leaders of congressional judiciary committees of any time he rejected a proposed action by Mueller because he deemed it "inappropriate or unwarranted" under department policy.
But before joining the Justice Department as Sessions' chief of staff, Whitaker appeared on CNN where he said the attorney general has the power to cut Mueller's budget and bring the investigation to a halt.
"Why is the President making this change and who has authority over Special Counsel Mueller's investigation?"
A Kremlin spokesman, Dmitry Peskov, on Thursday called Mueller's investigation a "headache" for USA authorities but said it "has nothing to do with us", and he declined to comment on Sessions' departure.
The special counsel's office upheld a long-standing Justice Department guideline that calls for discretion in taking legal or law enforcement measures within 60 days of an election in an effort to avoid the impression of attempting to sway voters.